The invention relates to a driver assistance system for a vehicle, including a detection device which is configured to detect driving data which characterizes the driving state of the vehicle and a controller which is designed to process the driving data detected by the detection device and, if predetermined driving data is present, to cause a brake device to carry out autonomous braking of the vehicle, and to a method for braking a vehicle including detecting driving data characterizing the driving state of the vehicle, by a detection device and processing the detected driving data and, if predetermined driving data is present, carrying out autonomous braking of the vehicle by the brake device.
A related art driver assistance system or method for braking a vehicle is known from EP 2 214 940 B1. In the related art driver assistance system, autonomous emergency braking of a vehicle with maximum available braking force is triggered by the service brake, independently of the driver, if the circumstances require it. If the vehicle has then come to a stationary state owing to the emergency braking, a device for detecting the vehicle in front checks whether a vehicle is located in front of the vehicle which has braked to a stationary state. If this is the case, a parking brake of the vehicle is applied. This is intended to prevent the vehicle which has been braked by emergency braking from being pushed into the vehicle in front by a vehicle driving behind. However, this assumes that the device for detecting the vehicle in front has not been damaged in an impact with the vehicle in front which, however, cannot be ruled out in the event of a collision occurring with the vehicle in front, despite the emergency braking which has been initiated.
Furthermore, driver assistance systems such as an ACC (Adaptive Cruise Control) system are also known from the related art. These systems measure the distance from a vehicle driving in front using a corresponding detection device and signal said distance to a controller, which then adjusts the actual distance from the vehicle driving in front to a speed-dependent setpoint distance by intervening in an engine controller and/or in a brake device. However, in the known ACC systems, this adjustment is only effective for as long as the detection device, for example a distance sensor, functions. In the cases in which the difference in speed from the vehicle driving in front has, however, become so large or the distance from the latter is so short that there is a high probability that an impact has to be expected, damage to the distance sensor must be expected because said sensor is generally arranged right at the front on the vehicle. However, owing to the detection device which is then defective, no intervention of the brake device takes place anymore, with the result that the movement energy of the affected vehicle is then dissipated only by the deformation work which is based on the collision with the vehicle driving in front.
In contrast to the above, the invention is based on the object of developing a driver assistance system or a method for operating a brake device of the type mentioned at the beginning in such a way that the consequences of an accident when there is a collision with an obstacle are alleviated.
In autonomously intervening ACC systems according to the related art, the detection device in the form of a distance sensor is generally destroyed when there is a collision with an obstacle, for example with a vehicle driving ahead. For this reason, the distance control system and therefore autonomous braking which is already initiated by the control device of the ACC system are aborted.
According to an aspect of the invention, a driver assistance system includes a detection device which is configured to detect driving data which characterizes the driving state of the vehicle, as well as a controller which is designed to process the driving data detected by the detection device, and, if predetermined driving data is present, to cause a brake device to carry out autonomous braking of the vehicle. However, in contrast to the related art, the controller is also designed such that when driving data which indicates a directly imminent collision with an obstacle is detected, the controller monitors the function of the detection device, and if the detection device no longer supplies any driving data or any plausible driving data to the controller, brings about continuation of the autonomous braking at least until the vehicle has been decelerated to a predefined speed.
According to another aspect of the invention, a method for braking a vehicle includes detecting, by a detection device, driving data characterizing the driving state of the vehicle, processing the detected driving data and, if predetermined driving data is present, carrying out autonomous braking of the vehicle by the brake device. If driving data which indicates an immediately imminent collision with an obstacle is detected by the detection device, the function of the detection device is monitored, and if the detection device no longer supplies any driving data or any plausible driving data the autonomous braking is continued at least until the vehicle has been decelerated to a predefined speed.
An “obstacle” is understood to mean here any obstacle which is suitable for colliding with a vehicle owing to a movement of said vehicle. For example, an “obstacle” is to be understood as meaning a vehicle which is driving in front or a stationary vehicle which is located in the movement path of the vehicle.
“Autonomous braking” is to be understood as meaning braking which is not initiated by the driver but rather by the driver assistance system. Furthermore, the predefined (lower) speed, to which the vehicle is decelerated by the brake device which is still kept applied even after a collision with the obstacle, is preferably the stationary state of the vehicle, that is to say a speed which is equal to zero. However, since speed sensors have been found empirically to be incapable of detecting precisely speeds below approximately 3 km/h to 5 km/h or of differentiating such a low speed from a stationary state, the predefined speed can also be this empirical value of the detection limit from 3 km/h to 5 km/h. The predefined speed up to which the vehicle is to be decelerated by the still applied brake device even after a collision with the obstacle can be any speed which is less than the speed of the vehicle which is present immediately before the collision with the obstacle. Even then, a deceleration which acts beyond the time of the collision and which goes beyond the intervention by the brake device is still present. The value of this predefined speed is defined by a person skilled in the art on the basis of empirical values.
The plausibility of the driving data supplied by the detection device, such as for example the actual distance from the vehicle in front, can be checked, for example, by comparison with the data supplied by further sensors, such as wheel rotational speed sensors, acceleration sensors, etc. Last but not least, redundant distance sensors whose measured values are compared with one another are also conceivable.
If the detection device can no longer supply any driving data or any plausible driving data at all, integrated algorithms of the driver assistance system determine a collision with the obstacle or with the vehicle driving in front. In this context, assumptions based, in particular, on statistical experiences can be made. In this case, the autonomous braking which is initiated by the driver assistance system, for example on the basis of an excessively short distance and/or on the basis of an excessively high speed relative to the obstacle even before the collision, is also continued after the collision until the vehicle has been decelerated to the predefined speed or to a stationary state.
However, if the detection device has not suffered any damage as a result of the collision and continues to supply plausible driving data, representing reality, to the controller, the driver assistance system can maintain, uninterruptedly per se on the basis of the distance from the vehicle in front or from the obstacle which has then shrunk, for example, to a very small value or to zero, the autonomous braking on the basis of the control algorithms, without a further intervention having to take place. This is because in this case the objective of autonomous or automatic braking which is carried out uninterruptedly at least until the predefined speed is reached or until the stationary state is reached is also achieved.
The advantage of these measures is that in the event of damage to the detection device by a collision which results in the detection device then no longer being able to supply any plausible driving data or any driving data at all to the controller, autonomous braking, which has already been previously initiated by the driver assistance system, is continued uninterruptedly until the vehicle has reached the predefined speed or the stationary state. As a result, the brake device can still contribute to dissipating kinetic energy even after a collision with an obstacle, such as a vehicle driving in front or a stationary vehicle, has already taken place, which kinetic energy would otherwise only be dissipated through elastic and plastic deformation of the crush zones of the parties of the collision. The brake device can therefore contribute to decelerating the vehicle driving up from behind, even after a rear end collision with a vehicle driving in front. This is important in particular in the case of a rear end collision at the end of a traffic jam, because the kinetic energy of the vehicle which is driving up from behind at the end should be dissipated as quickly as possible in order to avoid vehicles being pushed onto or into one another by the impact. Overall, embodiments of the invention therefore contribute to alleviating the consequences of accidents in the case of such collisions.
The controller is particularly preferably also designed in such a way that even after the autonomous decelerating of the vehicle to the predefined speed or to the stationary state, it keeps the brake device applied and/or applies a further brake device in order to keep the vehicle in the braked state. The advantage of keeping in a braked state the vehicle which is already in the stationary state after the collision with, for example, a vehicle in front is that the vehicle which is kept in a braked state then provides greater resistance with respect to vehicles which subsequently drive up from the rear, and therefore with respect to the tendency that the vehicle is pushed onto the vehicle in front by the impact.
According to one variant of this measure, the brake device which brakes the vehicle autonomously to the stationary state is a service brake device of the vehicle. The further brake device which then keeps the vehicle in the stationary state can be a parking brake device of the vehicle. In this case, the securing braking force is therefore transmitted from the service brake device to the parking brake device. This variant can be carried out easily particularly if the parking brake device can be controlled or activated by electrical signals which are then modulated, for example, by the controller of the driver assistance system.
According to a further variant, the vehicle can both be braked autonomously to the stationary state by the service brake device and subsequently kept in the braked state by the service brake device. This variant is suitable, in particular, for vehicles in which the parking brake device can only be activated mechanically.
The controller is also particularly preferably designed in such a way that it changes the brake device from the applied state to the released state if a (bifunctional) activation element such as, for example, an accelerator pedal or a clutch pedal of the vehicle has been activated. This applies both to the phase in which the deceleration of the vehicle which has been initiated by the driver assistance system still persists and to the phase in which the vehicle has already been braked to the predefined speed or to the stationary state and secured there. In both phases, the driver is to be provided with the possibility of aborting the autonomous braking at his own volition. This can be advantageous, for example, when after a collision it appears necessary to move the vehicle out of a danger zone if the drive system is still functionally capable, in order, for example, to avoid vehicles driving into the stationary vehicle from the rear by moving the vehicle onto a hard shoulder. However, the activation element can also be a monofunctional activation element, such as a pushbutton key, which is then provided exclusively for the purpose of aborting the autonomous braking.
In addition to the described intervention into the brake device, customary driving assistance systems such as ACC additionally also have the possibility of intervening in the controller of the drive machine. According to one preferred development, the controller of the driver assistance system can therefore be designed in such a way that, in addition to the intervention in the brake device of the vehicle, if predetermined driving data is present, a controller of a drive machine is made to reduce the driving power autonomously. If driving data which indicates an immediately imminent collision with an obstacle is detected, the function of the detection device is then monitored as described, and if the detection device no longer supplies any driving data or any plausible driving data to the controller, in addition to the continuation of the autonomous braking a continuation of the autonomous reduction of the driving power of the drive machine is also brought about, at least until the vehicle has been decelerated to the predefined speed. In this case, the drive machine also contributes with its drag torque to decelerating the vehicle after a collision has taken place.
The power of the drive machine is preferably reduced, for example, as far as an idling rotational speed driving power, but the drive machine is not completely switched off so that the brake device releases the vehicle, as described above, as a result of activation of the accelerator pedal and the vehicle can be set in motion again under its own force in so far as or for as long as this is still possible after the collision.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more exemplary embodiments when considered in conjunction with the accompanying drawings.